The invention relates to laminated rotor structure for a dynamoelectric machine and to a method for manufacturing such structures. More particularly, the invention relates to a laminated rotor structure formed of a plurality of groups of rotor laminations that are held in spaced relationship by a plurality of laminated spacer assemblies which also serve to seal conductor-receiving passageways through the rotor from axial coolant ducts, thereby to enable molten metal to be poured into the conductor-receiving slots to form cast conductors in the rotor. The laminated plates of each of the spacer assemblies are secured in desired fixed relationship to one another and in predetermined fixed relationships with respective groups of rotor laminations on which sets of the spacer assemblies are mounted. In the method of the invention the laminations or plates of each spacer assembly are formed in two or three different configurations to enable the spacer assemblies to be reliably and economically manufactured and assembled in desired operating positions on predetermined, and suitably pre-formed, rotor laminations.
Heretofore a number of different dynamoelectric machine rotor structures and associated methods of manufacture were well known for producing rotors that employ cast conductors in combination with radial cooling ducts through the rotors and past such conductors. A common early form of such prior art used casting pins between selected groups of rotor laminations to contain molten conductor metal in conductor-receiving passageways and seal it from associated areas of radial coolant ducts when the molten metal is poured into the passageways to cast the conductors. After that type of casting operation, the pins would be removed from between the groups of laminations thus leaving voids that define cooling passageways around the conductors and between the groups of laminations. An example of such a prior art structure is shown in U.S. Pat. No. 2,504,824, which issued on Apr. 18, 1959. A related prior art approach is shown in U.S. Pat. No. 2,486,798, which issued on Nov. 1, 1949. In that second patent a plurality of removable metal clips are used to hold groups of rotor laminations in spaced relationship while conductors are cast in the rotor. After the casting operation the clips are stripped from the rotor.
Alternative methods of forming such cast rotors are shown in U.S. Pat. Nos. 2,370,458 which issued Feb. 27, 1945 and 2,504,823 which issued Apr. 19, 1950 and 2,607,969, which issued Aug. 26, 1952. In each of these patents, a plurality of groups of rotor laminations are spaced apart by destructible molds formed of plaster of Paris or other relatively easily removable material, such as cardboard. The destructible or removable materials act to block molten metal from the areas of the rotors that are to serve as coolant ducts after conductors have been cast in place in conductor slots extending axially through the rotor laminations. Although the use of such casting forms eliminates the requirement of placing, then subsequently removing, a large number of casting pins, as was required by the type of rotor forming operations characterized by the first group of patents noted above, such removable spacers also involve inherent disadvantages. In addition to the high cost of forming, then subsequently removing such molding materials from between groups of rotor laminations, such manufacturing techniques have the further disadvantage that no permanent mechanical spacer, other than portions of the cast conductors, are left in the rotor assembly to secure the respective groups of laminations in their desired spaced relationship.
In order to overcome such disadvantages, later rotor manufacturing techniques were developed, which employed permanent spacers between groups of rotor laminations. Examples of such later rotor structures are shown in U.S. Pat. Nos. 2,956,186, which issued Oct. 11, 1960 and 3,166,804 which issued Jan. 26, 1965 and 3,462,625 which issued Aug. 19, 1969. In the respective inventions shown in these latter three patents, a plurality of metal spacers are mounted between groups of rotor laminations and around conductor passageways through the laminations to simultaneously hold the groups of laminations in spaced relationship and prevent molten conductor metal from entering portions of the coolant ducts through the rotor. Such manufacturing techniques and resultant structures involve the inherent disadvantage that they require the use of a large number of separate parts to form a rotor, and also result in the risk that some of the plurality of spacing loops or clips may be thrown from the rotor when it is operated. Of course, any such undesirable movement of such spacing clips between the groups of rotor laminations could cause the clips to wedge between the rotor and an associated stator thereby causing extensive damage to a machine.
In earlier prior art devices, in order to avoid such movement of rotor lamination spacing means, it was at one time a common practice to weld such spacers and coolant duct forming means in position on the respective groups of laminations. An example of such prior art welding techniques and associated laminated rotor structure is shown in U.S. Pat. No. 2,176,870 which issued on Oct. 24, 1939. Of course, the expense of forming such a plurality of welds in a rotor assembly constitutes a major disadvantage of that type of prior art arrangement. One form of known prior art structure that avoids the use of such welds, while providing convenient means for quickly and accurately positioning a plurality of rotor lamination spacers between selected groups of laminations in order to hold them in spaced relationship, while at the same time providing means for blocking molten conductor metal from flowing into coolant ducts of the rotor assembly, is shown in U.S. Pat. No. 2,504,825 which issued on Apr. 18, 1950. In that patent a plurality of laminated spacer assemblies are each formed with an integral annular band that positions respective teeth of the assembly in desired fixed relationship so that the assemblies can be readily stacked in position between groups of rotor laminations. After molten conductors are cast in passageways defined by apertures through the main rotor laminations and aligned apertures in the respective teeth of the spacer assemblies, the annular positioning portions of each of the spacer assemblies are machined away so that the teeth remain locked in position in the rotor assembly. A disadvantage of such a prior art structure and manufacturing method is that no convenient means are disclosed for readily and accurately positioning the respective teeth relative to each conductor-receiving aperture in the rotor laminations, except for the annual holding rings associated with the teeth. Of course, the cost of separately machining away the integral teeth-holding rings is a further disadvantage of such a prior art manufacturing process. That prior art patent also makes brief reference to the fact that such laminated spacer teeth may be held in position, prior to a conductor-casting operation, by a suitable jib, in lieu of using an integral annular positioning member associated with the respective teeth. A major disadvantage of such a jib process is that a large number of separate pieces are necessarily required to assemble a given rotor lamination spacer. Moreover, the mounting of such a jib during a casting operation, and its subsequent removal from the cast rotor, would increase manufacturing costs.
Some of the disadvantages of the prior art types of inventions discussed above can be avoided by using a plurality of differently configured sets of rotor laminations to build up desired coolant passageways through a rotor, while at the same time providing means for defining fluid-tight passageways through the rotor in which moltent conductor metal can be poured to cast conductors. Examples of such prior art devices, using a plurality of differently configured groups of rotor laminations, is shown in U.S. Pat. Nos. 890,577, issued June 9, 1908 and 2,944,171 issued July 5, 1960 and 3,684,906 issued Aug. 15, 1972 and assigned to the assignee of the invention of the present application. While this general type of rotor construction has been found desirable for many applications, it necessarily involves the use of a plurality of different configurations of rotor laminations; thus, the expense of manufacturing such rotors is undesirably increased by the requirements of different types of dies to make the respective laminations and by the need to store supplies of the different configurations of laminations, as well as by the added expense required to carefully arrange the groups of laminations in proper sequence while practicing such a manufacturing process.
As can be understood from the brief description of the number of prior art dynamoelectric machine rotor structures and manufacturing methods given above, it would be desirable to provide a rotor structure and manufacturing process that avoids the disadvantages associated with each of those prior art devices and processes. Accordingly, it is a primary object of the present invention to provide a laminated rotor structure having cast conductors and radial coolant ducts, and including permanent spacer assemblies between groups of rotor laminations, while at the same time overcoming or avoiding the types of disadvantages discussed above with reference to the prior art inventions disclosed in the respective patents noted above.
Another object of the invention is to provide a method of manufacturing a laminated rotor having laminated spacer assemblies mounted in the rotor between groups of main rotor laminations and locked in fixed relationship to the groups of rotor laminations by commercially feasible and relatively inexpensive mounting means that reliably secure the spacing assemblies against movement relative to the main rotor laminations.
A further object of the invention is to provide a method for manufacturing a laminated rotor assembly in which a plurality of laminated spacer assemblies are efficiently produced on high speed punching machines, stacked into spacer assemblies of predetermined size, and staked together to form easily usable components for fabricating a rotor assembly.
Additional objects and advantages of the invention will become apparent to those skilled in the art from the description of the invention presented herein considered in conjunction with the accompanying drawings.